The present work deals with two general areas of vagal control of breathing: 1. Response of Respiratory Phase Switching Mechanisms to Vagal Stimulation - this is a part of a broad project which aims to define the response characteristics of the switching mechanisms by examining the changes in their excitability during the following well-controlled inputs from different sources; i.e., vagal, intercostal, sympathetic, pontine and somatic inputs. The studies are done primarily in pentobarbital anesthetized cats. 2. Role of Vagal Volume-Related Feedback in Control of Breathing Pattern in Man - in the past two years we have documented the presence of an important vagal modulation of breathing in normal man under enflurane anesthesia. Vagal influence appears to be critically dependent on the magnitude of inspiratory duration in the absence of volume feedback (Tiocc). Confidence limits for the relation between spontaneous Ti and Tiocc in normal subjects have been established. Additionally, we found that vagal influence is generally depressed in patients with obstructive airway disease and is slightly augmented in patients with restrictive lung disease. In the remaining year of this grant the project will be limited to the study of patients with specific cardio-pulmonary disorders.